Communications equipment must typically be tested in order to verify proper performance. Such testing can include, for example, development testing, wherein proper functioning of a prototype of a candidate design is verified; acceptance testing, where it is confirmed that an individual component or piece of equipment functions according to specifications; or ongoing field tests, where correct functioning of equipment in the field is monitored. Such testing may be performed, for example, by external test equipment or by built-in self-test (BIST) capability.
One manner of testing communications equipment is to subject the equipment to test patterns that simulate the type of data that the equipment will be handling in use. For example, the Optical Internetworking Forum (OIF) document entitled “Common Electrical I/O (CEI)—Electrical and Jitter Interoperability agreements for 6G+ bps and 11G+ bps I/O,” numbered IA # OIF-CEI-01.0, and dated Dec. 13, 2004, specifies a Jitter Tolerance Pattern having a 72 zero consecutive identical digit (CID) portion. followed by at least 10328 bits of a standard pseudo random bit sequence (PRBS) polynomial designated as PRBS31, with an appropriate seed (all ones). This is followed by a complementary portion, i.e., a CID portion of 72 ones and the complement of the PRBS bits, again with appropriate seeding (all ones and thus not complementary to the first seed). The PRBS31 polynomial is specified in International Telecommunication Union ITU-T 0.150 section 5.8. The fixed patterns specified in standards such as those just mentioned may have limited diagnostic value under certain conditions; the specified Jitter Tolerance Pattern is relatively low density and has a no-activity CID.
Accordingly, it would be desirable to provide an apparatus and method where more flexible test patterns can be employed. Such patterns can be more exploitive than a fixed standard pattern, that is, they can subject the equipment under test to more difficult conditions than standard patterns, and thus enhance error diagnostic capabilities; for example, with respect to tolerance of jitter.